Gas production potential of disperse low-saturation hydrate accumulations in oceanic sediments

In this paper, we evaluate the gas production potential of disperse, low-saturation (S-H < 0.1) hydrate accumulations in oceanic sediments. Such hydrate-bearing sediments constitute a significant portion of the global hydrate inventory. Using numerical simulation, we estimate (a) the rates of gas production and gas release from hydrate dissociation, (b) the corresponding cumulative volumes of released and produced gas, as well as (c) the water production rate and the mass of produced water from disperse, low-S-H hydrate-bearing sediments subject to depressurization-induced dissociation over a 10-year production period. We investigate the sensitivity of items (a)-(c) to the following hydraulic properties, reservoir conditions, and operational parameters: intrinsic permeability, porosity, pressure, temperature, hydrate saturation, and constant pressure at which the production well is kept. The results of this study indicate that, despite wide variations in the aforementioned parameters (covering the entire spectrum of such deposits), gas production is very limited, never exceeding a few thousand cubic meters of gas during the 10-year production period. Such low production volumes are orders of magnitude below commonly accepted standards of economic viability, and are further burdened with very unfavorable gas-to-water ratios. The unequivocal conclusion from this study is that disperse, low-S-H hydrate accumulations in oceanic sediments are not promising targets for gas production by means of depressurization-induced dissociation, and resources for early hydrate exploitation should be focused elsewhere. (C) 2007 Elsevier Ltd. All rights reserved.